Effect of Different Flaw Sizes and Surface Treatment on Biaxial Flexural Strength of Feldspathic Porcelain

Background and Objectives: Porcelain restorations are often ground for recontouring and occlusal adjustments. This removes the surface glaze layer and causes flaws that can grow in wet environments due to stress corrosion cracking and decrease the strength of porcelain and subsequently the longevity and clinical service of restoration. The aim of this study was to assess the effect of flaw size and surface treatments on biaxial flexural strength of feldspathic porcelain.

Materials and Methods: Eighty feldspathic porcelain discs were fabricated, polished (P2000) and divided into two series (n=40) each with four subgroups (n=10); three subgroups in each series were centrally indented by means of a Vickers hardness tester under a load of either 9.8 N (A series) or 29.4 N (B series) and were then subjected to no surface treatment (subgroups 2 and 6), polishing (subgroups 3 and 7) or polishing plus silane plus resin (subgroups 4 and 8). Ten specimens in each series were not indented as controls (subgroups 1 and 5). Biaxial flexural strength of the discs was tested after water storage for 48 hours and the data were analyzed by two-way ANOVA and Tukey’s HSD test.

Results: Both control subgroups revealed significantly higher strength than other subgroups (P<0.05) but there was no significant difference among other subgroups (P>0.05). The mean flexural strength of indented subgroups in B series was significantly lower than that in the same subgroups in A series (P<0.05).

Conclusion: Presence and size of flaws affect the flexural strength of porcelain. Within the limitations of this study, none of the surface treatments could strengthen the cracked ceramic.